Glass fibers for use in composite applications are manufactured from various raw materials combined in specific proportions to yield a desired chemical composition. This proportion is commonly termed a “glass batch.” The composition of the glass batch and the glass manufactured from it are typically expressed in terms of percentages of the components, which are expressed as oxides. SiO2, Al2O3, CaO, MgO, B2O3, Na2O, K2O, Fe2O3, and minor amounts of other oxides are common components of a glass batch. Numerous types of glasses may be produced from varying the amounts of these oxides, or eliminating some of the oxides, in the glass batch. Examples of such glasses that may be produced include E-glass, S-glass, R-glass, A-glass, C-glass, and ECR-glass. The glass composition determines the properties of the glass including properties such as the viscosity, the liquidus temperature, the durability, the density, the strength, and the Young's modulus of the glass. Non-physical considerations given to commercial glass compositions include the raw material cost and environmental impact caused by manufacturing the glass.
E-glass compositions are the most common glass compositions for making continuous glass fiber strands used in textile and reinforcement applications. One advantage of E-glass is that its liquidus temperature is approximately 200° F. below its forming temperature, which is commonly defined as the temperature at which the viscosity of the glass equals 1000 poise. E-glass has a wide range of forming temperatures and a low devitrification rate. Historically, commercial E-glass compositions possessed forming temperatures between 2150° F. and 2350° F. and liquidus values from approximately 100° F. to 250° F. below the forming temperature.
The most common high strength glass compositions for making continuous glass fiber strands are “S-Glasses.” S-Glass is a family of glasses composed primarily of the oxides of magnesium, aluminum, and silicon with a chemical composition that produces glass fibers having a higher mechanical strength than E-Glass fibers. S-glasses generally have compositions that were originally designed to be used in high-strength applications such as ballistic armor. Some examples of S-Glasses include XStrand® S, FliteStrand® S, and ShieldStrand® S by Owens Corning, having a Young's modulus of about 88 GPa. Another example is S-2 Glass® by AGY, which is an S-Glass that may have a Young's modulus of approximately 89.6 GPa (13 MPSI).
Many glasses having high mechanical strengths can be very costly to produce, because of their high forming temperatures and due to other process constraints. In addition, many glasses having high mechanical strength may not be soluble in biological fluids. The lack of solubility in biological fluids can limit the product forms that are acceptable to the customer. Thus, there remains a need in the art for improved glass compositions and methods of making such glasses that provide high mechanical strength having the advantage of being soluble in biological fluids.